• The content and format of this book was extensively field tested by hundreds of undergraduate students at Indiana University throughout the revision process.

• Key concepts are highlighted in each chapter, so that the topics being developed are stated concisely.

• Factual content has been updated throughout.

• A new chapter has been added to the fourth edition -Genomics and Proteomics Drive Information-Age Biology (Chapter 13)

• Chapters 12 and 14 in the third edition, "Bacteriophage" and "Plasmids and Transposons" have been merged into one chapter (Chapter 14).

• A Postscript has been added that reviews the most surprising developments in molecular biology over the past two decades and dares to look ahead to potential discoveries. The Prologue also provides tips for students who want to continue their study of molecular biology.

• Progression diagrams at the beginning of the chapters serve as a "road map" for the student.

• A layering approach to knowledge construction is employed, developing complexity chapter-by-chapter, rather than presenting a series of detail-laden descriptions all at once.